WASHINGTON (AP) - President Barack Obama on Wednesday launched the most sweeping effort to curb U.S. gun violence in nearly two decades, announcing a $500 million package that sets up a fight with Congress over bans on military-style assault weapons and high-capacity ammunition magazines just a month after a shooting in Connecticut killed 20 school children.

Obama signed 23 executive actions, which require no congressional approval. But the president, speaking at the White House, acknowledged the most sweeping, effective actions must be taken by lawmakers.

The president appealed to the nation's conscience, but his announcement promises to lead to a bitter fight with a powerful pro-gun lobby that has long warned supporters that Obama wanted to take away their guns.

The U.S. has the highest rate of gun ownership of any country in the world, and pro-gun groups see any move on gun restrictions as an offense against the right guaranteed by the Second Amendment of the U.S. Constitution. Critics counter that the country's founding fathers never could have foreseen assault weapons more than two centuries ago, when guns were intended for the common, not individual, defense, guns were often stored in community areas and rifles fired one laborious shot at a time.

"This is the land of the free and the home of the brave, and always will be," Obama said, acknowledging the right to possess and bear firearms. "But we've also long realized ... that with rights come responsibilities."

Obama was joined by children who wrote him letters about gun violence in the weeks following the Connecticut shooting. Families of the children killed in the shooting, as well as survivors, were also in the audience.

Emotions have been high since the Connecticut shooting, which Obama has called the worst day of his presidency. He largely ignored the issue of gun violence during his first term but appears willing to stake his second term on it now. He'll have to contend with looming fiscal issues that have threatened to push whatever he proposes aside, at least for a while.

Gun control advocates also worry that opposition from the powerful National Rifle Association and its allies in Congress will be too great to overcome.

"Attacking firearms and ignoring children is not a solution to the crisis we face as a nation," the NRA said in a statement after Obama's announcement. "Only honest, law-abiding gun owners will be affected and our children will remain vulnerable to the inevitability of more tragedy."

The NRA also released an online video Tuesday that called Obama an "elitist hypocrite" for having armed Secret Service agents protect his daughters at school while not committing to installing armed guards in all schools. The NRA insists that the best way to prevent more mass shootings is to give more "good guys" guns.

The White House called the NRA video "repugnant and cowardly."

Obama's proposals are aimed at gun violence in general, not just mass shootings. He said more than 900 Americans have been killed by guns in the month since the Connecticut shooting.

"Every day we wait, the number will keep growing," he said.

The public appears receptive to stronger federal action on guns. Nearly six in 10 Americans want stricter gun laws in the aftermath of the Connecticut shooting, according to a new Associated Press-GfK poll. Three-quarters of Americans said they reacted to the Connecticut shooting with deep anger, while 54 percent said they felt deeply ashamed it could happen in the United States.

The poll also shows 51 percent said they believed laws limiting gun ownership infringe on the public's right to bear firearms.

White House officials, seeking to avoid setting the president up for failure, have emphasized that no single measure -- even an assault weapons ban -- would solve the scourge of gun violence. But without such a ban, or other sweeping Congress-approved measures, it's unclear whether executive actions alone can make any noticeable difference.

The office of the most powerful Republican in Congress, House of Representatives Speaker John Boehner, signaled no urgency to act on the proposals. "House committees of jurisdiction will review these recommendations," Boehner spokesman Michael Steel said. "And if the Senate passes a bill, we will also take a look at that."

Senate Majority Leader Harry Reid, a fellow Democrat, called Obama's package "thoughtful recommendations" and said the Senate would consider legislation addressing gun violence early this year.

The president asked Congress to renew the ban on high-grade, military-style assault weapons that was first signed into law by President Bill Clinton in 1994 but expired in 2004. Obama also called for limiting ammunition magazines to 10 rounds or fewer, and he proposed a federal statute to stop purchases of guns by buyers who are acting for others.

The president also called for a focus on universal background checks. Some 40 percent of gun sales take place without background checks, including those by private sellers at gun shows or over the Internet, according to the Brady Campaign to Prevent Gun Violence.

The president's framework is based on recommendations from Vice President Joe Biden, who led a wide-ranging task force on gun violence. Beyond the gun control measures, Biden also gave Obama suggestions for improving mental health care and addressing violent images in video games, movies and television.

The president also called for improvements in school safety, including putting 1,000 police officers in schools.

States and cities have been moving against gun violence as well. New York Gov. Andrew Cuomo on Tuesday signed into law the toughest gun control law in the U.S., and the first since the Connecticut shooting. The law includes a tougher assault-weapons ban and provisions to try to keep guns out of the hands of mentally ill people who make threats.

The NRA criticized the bill, saying in a statement, "These gun control schemes have failed in the past and will have no impact on public safety and crime."

In Washington, it's unclear how much political capital Obama will use in pressing for congressional action.

The White House and Congress will soon be consumed by three looming fiscal deadlines, each of which is expected to be contentious. And the top Republican in the Senate, Mitch McConnell, has warned the White House that it will be at least three months before the chamber considers gun legislation.

Congress, in any case, can move slowly. The chairman of the Senate Judiciary Committee said Wednesday he'll begin hearings in two weeks on gun safety proposals. Democratic Sen. Patrick Leahy, a gun owner, said he envisions a series of hearings examining violence in popular media and how to keep guns safe, among other topics.

Leahy's plan could take more time than Obama has urged.

Obama's long list of executive orders includes the following:

Ordering tougher penalties for people who lie on background checks and requiring federal agencies to make relevant data available to the federal background check system.

Ending limits that make it more difficult for the government to research gun violence, such as gathering data on guns that fall into criminal hands.